Anthropogenic habitat interconnection provokes homogenization of allopatric freshwater fish: concordance of genetic and phenotypic evidence

Anthropogenic habitat alteration can rapidly disturb native fish species by hybridization with introduced species. In Korea, the construction of water conduits has unilaterally introduced the allopatrically separated fish species Cobitis tetralineata from the Seomjin River to the Dongjin River where its sister species C. nalbanti inhabits. To assess the impact of this secondary contact on the native species, we investigated the genetic and phenotypic characteristics of populations from the known hybrid zone and other river tributaries of the Dongjin River. Genetic studies of eight microsatellites, one mitochondrial gene, and five protein-coding nuclear genes showed a consistent admixture pattern. Multivariate morphological analysis with 29 meristic and morphometric characters exhibited hybrid populations’ morphological intermediacy to their two parental species. However, all the tributaries being confluent downstream of the Dongjin River were free from hybridization, protecting the native purebred species from the risk of genomic extinction. The present study calls attention to a genetic survey throughout the whole distributional range of native fish species to identify the location containing purebred natives and to evaluate the extent of hybridization, and helps set a conservation priority to prevent further expansion of the current genetic invasion.